Vehicles having a hybrid drive structure mostly have an internal combustion engine as a first drive unit and an electric machine or a hydraulic motor as a second drive unit. Further drive units are also possible. Thus, during operation of the hybrid vehicle, the drive torque may be applied jointly by the drive units.
In such a hybrid system, the combustion engine is disconnected from the power train and stopped at specific operating points, through which, in addition to lower exhaust-gas emissions, a lower fuel consumption occurs. The vehicle moves purely electrically, due to the motively-connected, electric machine and the energy for operating the electric machine, which is stored in a high-voltage battery. By switching the electric machine over into a generative mode, power is fed back into the high-voltage battery when the combustion engine is recoupled to the power train, which means that the high-voltage battery is charged. However, charging of the high-voltage battery is also possible when the combustion engine is uncoupled. In order to perform the automatic charging and discharging operations, an operating strategy is stored in the specific control unit.
Starting out from the specific operating strategy, a torque of the electric machine that is applied by the electric machine is calculated as a drive torque by the control unit of the electric machine. This calculated torque must be highly accurate, in order to render possible an optimum manner of operation of the power train made up of the combustion engine and the electric machine, in particular, during hybrid operation of the motor vehicle.
A method, in which a continuous torque comparison takes place within one monitoring level in a vehicle control unit, is described in German Patent Application No. DE 10 2005 062 870 A1. In this context, a permissible torque is ascertained. Using a torque-range check, it is determined if the ascertained setpoint torque is within torque ranges of two separate drive units.